The present invention relates to a DMD (Digital Micromirror Device) projector, and in particular, to an optical system of the DMD projector.
Heretofore, an extra-high pressure mercury lamp, a xenon lamp or the like having a light source by heat has been employed for a source of illumination in a conventional DMD projector.
Meanwhile, in the field of transmissive liquid crystal projectors, a liquid crystal projector has been proposed in Japanese Patent Application Laid-Open No. 2001-249400. In the liquid crystal projector, a liquid crystal panel has to be illuminated with linear polarization. When it is illuminated with natural light, only a part of rays of the natural light is used as illumination owing to a polarization plate placed just before the liquid crystal panel. Accordingly, the liquid crystal panel becomes dark. In addition, the rays that are not used as illumination lead to an increase in temperature of the liquid crystal panel.
Since the conventional DMD projector is provided with the source of illumination by heat as described above, its conversion efficiency from input power to light is low. Consequently, the DMD projector requires a larger input power, a large-sized power source and lamp (mostly provided with a reflecting mirror), a cooling fan and the like. Accordingly, the DMD projector increases in weight and the life of a DMD panel is shortened owing to the heat.
In another conventional 1-chip-type DMD projector, an illumination optics system for color display is provided with a rotary color filter, also named as a color wheel, and images in respective colors are sequentially displayed (time-division-color-displayed) by synchronizing the rotation of the color wheel with on/off signals of respective pixels of a DMD panel so that normal color images can be produced to the human eye due to the effect of afterimages. However, the DMD projector has the problem that the sound generated when driving a rotating motor for the color wheel becomes a source of noise at a constant level.
Besides, even when LEDs (Light Emitting Diodes) having high light conversion efficiency are employed to reduce the input power, a screen onto which a picture is projected may become dark. In that event, the object of the projector cannot be accomplished.
Moreover, the conventional projector is indispensably provided with an AC100V power source for a light source by heat and for driving the cooling fan, the motor and the like. However, it has been a task to achieve the projector driven by a battery to offer a mobile projector.
It is therefore an object of the present invention to provide a DMD projector and an optical system thereof employing LEDs for a bright projection screen, wherein input power for illumination is drastically reduced, and a power source and a light source are significantly reduced in size and weight as well as extending the life of a DMD panel to the same level as that of micro solid-state devices.
According to a first aspect of the present invention, for achieving the objects mentioned above, there is provided a digital-micromirror-device projector for displaying color images by synchronizing respective on/off signals of red, green and blue with on/off signals of the pixels of the digital-micromirror-device panel, comprising:
light emitting diode arrays for red, green and blue;
first fly-eye lenses disposed in contact with the light emitting diode arrays;
second fly-eye lenses disposed at a distance from the first fly-eye lenses;
a cross dichroic prism into which lights of red, green and blue projected from the second fly-eye lenses enters through respective entrance planes for red, green and blue, and which projects synthesized light of red, green and blue through a remaining exit plane;
an illumination optical system for focusing and superposing extended images, which are of the same number as elements of the light emitting diode arrays, from exit pupils of respective element lenses of the first fly-eye lenses via the corresponding element lenses of the second fly-eye lenses and the subsequent illumination lenses on a digital-micromirror-device panel on the occasion of illuminating the digital-micromirror-device panel with the synthesized light projected from the cross dichroic prism; and
a projection optical system for focusing rays reflected from on-pixels of the digital-micromirror-device panel on a screen in response to on/off switch of pixels of the digital-micromirror-device panel.
According to a second aspect of the present invention, in the first aspect, dicroic mirrors of the cross dichroic prism are replaced by dichroic plane mirrors.
According to a third aspect of the present invention, in the first or second aspect, one side of the respective elements of the first fly-eye lenses disposed in contact with the light emitting diode arrays is aspherical to illuminate the plane of the digital-micromirror-device panel with high illuminance and high uniformity.
According to a fourth aspect of the present invention, in the first or second aspect, one side of the respective elements of the first fly-eye lenses disposed in contact with the light emitting diode arrays is spherical, whose curvature radius R mm, thickness of lens d mm, and refractive index n at a line e of wavelength satisfy the following three conditional expressions.
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According to a fifth aspect of the present invention, there is provided a digital-micromirror-device projector for displaying color images by synchronizing respective on/off signals of red, green and blue with on/off signals of the pixels of the digital-micromirror-device panel comprising:
light emitting diode arrays for red, green and blue;
first fly-eye lenses disposed in contact with the light emitting diode arrays, as well as in contact with or close to entrance planes for red, green and blue of a cross dichroic prism;
the cross dichroic prism into which lights of red, green and blue projected from the first fly-eye lenses enters through the respective entrance planes for red, green and blue, and which projects synthesized light of red, green and blue through a remaining exit plane;
a second fly-eye lens disposed in contact with or close to the exit plane of the cross dichroic prism for receiving the synthesized light of red, green and blue from the exit plane;
an illumination optical system for focusing and superposing extended images, which are of the same number as elements of the light emitting diode arrays, from exit pupils of respective element lenses of the first fly-eye lenses via the cross dichroic prism, the corresponding element lenses of the second fly-eye lens and the subsequent illumination lenses on a digital-micromirror-device panel on the occasion of illuminating the digital-micromirror-device panel with the synthesized light projected from the cross dichroic prism; and
a projection optical system for focusing rays reflected from on-pixels of the digital-micromirror-device panel on a screen in response to on/off switch of pixels of the digital-micromirror-device panel.
According to a sixth aspect of the present invention, in the fifth aspect, dicroic mirrors of the cross dichroic prism are replaced by dichroic plane mirrors.
According to a seventh aspect of the present invention, in the fifth or sixth aspect, one side of the respective elements of the first fly-eye lenses disposed in contact with the light emitting diode arrays is aspherical to illuminate the plane of the digital-micromirror-device panel with high illuminance and high uniformity.
According to an eighth aspect of the present invention, in the fifth or sixth aspect, one side of the respective elements of the first fly-eye lenses disposed in contact with the light emitting diode arrays is spherical, whose curvature radius R mm, thickness of lens d mm, and refractive index n at a line e of wavelength satisfy the following three conditional expressions.
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dxe2x89xa75.0xe2x80x83xe2x80x83(2)
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According to a ninth aspect of the present invention, there is provided an optical system used in the digital-micromirror-device projector as mentioned in any one of first to eighth aspects.